mktime.3p (5120B)
- '\" et
- .TH MKTIME "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH PROLOG
- This manual page is part of the POSIX Programmer's Manual.
- The Linux implementation of this interface may differ (consult
- the corresponding Linux manual page for details of Linux behavior),
- or the interface may not be implemented on Linux.
- .\"
- .SH NAME
- mktime
- \(em convert broken-down time into time since the Epoch
- .SH SYNOPSIS
- .LP
- .nf
- #include <time.h>
- .P
- time_t mktime(struct tm *\fItimeptr\fP);
- .fi
- .SH DESCRIPTION
- The functionality described on this reference page is aligned with the
- ISO\ C standard. Any conflict between the requirements described here and the
- ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
- .P
- The
- \fImktime\fR()
- function shall convert the broken-down time, expressed as local time,
- in the structure pointed to by
- .IR timeptr ,
- into a time since the Epoch value with the same encoding as that of the
- values returned by
- \fItime\fR().
- The original values of the
- .IR tm_wday
- and
- .IR tm_yday
- components of the structure shall be ignored, and the original values
- of the other components shall not be restricted to the ranges
- described in
- .IR <time.h> .
- .P
- A positive or 0 value for
- .IR tm_isdst
- shall cause
- \fImktime\fR()
- to presume initially that Daylight Savings Time, respectively, is or is
- not in effect for the specified time. A negative value for
- .IR tm_isdst
- shall cause
- \fImktime\fR()
- to attempt to determine whether Daylight Savings Time is in effect for
- the specified time.
- .P
- Local timezone information shall be set as though
- \fImktime\fR()
- called
- \fItzset\fR().
- .P
- The relationship between the
- .BR tm
- structure (defined in the
- .IR <time.h>
- header) and the time in seconds since the Epoch is that the result
- shall be as specified in the expression given in the definition of
- seconds since the Epoch (see the Base Definitions volume of POSIX.1\(hy2017,
- .IR "Section 4.16" ", " "Seconds Since the Epoch")
- corrected for timezone and any seasonal time adjustments, where the
- names other than
- .IR tm_yday
- in the structure and in the expression correspond, and the
- .IR tm_yday
- value used in the expression is the day of the year from 0 to 365
- inclusive, calculated from the other
- .BR tm
- structure members specified in
- .IR <time.h>
- (excluding
- .IR tm_wday ).
- .P
- Upon successful completion, the values of the
- .IR tm_wday
- and
- .IR tm_yday
- components of the structure shall be set appropriately, and the other
- components shall be set to represent the specified time since the Epoch,
- but with their values forced to the ranges indicated in the
- .IR <time.h>
- entry; the final value of
- .IR tm_mday
- shall not be set until
- .IR tm_mon
- and
- .IR tm_year
- are determined.
- .SH "RETURN VALUE"
- The
- \fImktime\fR()
- function shall return the specified time since the Epoch encoded as
- a value of type
- .BR time_t .
- If the time since the Epoch cannot be represented, the function shall
- return the value (\fBtime_t\fP)\-1
- and set
- .IR errno
- to indicate the error.
- .SH ERRORS
- The
- \fImktime\fR()
- function shall fail if:
- .TP
- .BR EOVERFLOW
- The result cannot be represented.
- .LP
- .IR "The following sections are informative."
- .SH "EXAMPLES"
- What day of the week is July 4, 2001?
- .sp
- .RS 4
- .nf
- #include <stdio.h>
- #include <time.h>
- .P
- struct tm time_str;
- .P
- char daybuf[20];
- .P
- int main(void)
- {
- time_str.tm_year = 2001 \(em 1900;
- time_str.tm_mon = 7 \(em 1;
- time_str.tm_mday = 4;
- time_str.tm_hour = 0;
- time_str.tm_min = 0;
- time_str.tm_sec = 1;
- time_str.tm_isdst = -1;
- if (mktime(&time_str) == -1)
- (void)puts("-unknown-");
- else {
- (void)strftime(daybuf, sizeof(daybuf), "%A", &time_str);
- (void)puts(daybuf);
- }
- return 0;
- }
- .fi
- .P
- .RE
- .SH "APPLICATION USAGE"
- None.
- .SH RATIONALE
- None.
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "\fIasctime\fR\^(\|)",
- .IR "\fIclock\fR\^(\|)",
- .IR "\fIctime\fR\^(\|)",
- .IR "\fIdifftime\fR\^(\|)",
- .IR "\fIgmtime\fR\^(\|)",
- .IR "\fIlocaltime\fR\^(\|)",
- .IR "\fIstrftime\fR\^(\|)",
- .IR "\fIstrptime\fR\^(\|)",
- .IR "\fItime\fR\^(\|)",
- .IR "\fItzset\fR\^(\|)",
- .IR "\fIutime\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "Section 4.16" ", " "Seconds Since the Epoch",
- .IR "\fB<time.h>\fP"
- .\"
- .SH COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
- from IEEE Std 1003.1-2017, Standard for Information Technology
- -- Portable Operating System Interface (POSIX), The Open Group Base
- Specifications Issue 7, 2018 Edition,
- Copyright (C) 2018 by the Institute of
- Electrical and Electronics Engineers, Inc and The Open Group.
- In the event of any discrepancy between this version and the original IEEE and
- The Open Group Standard, the original IEEE and The Open Group Standard
- is the referee document. The original Standard can be obtained online at
- http://www.opengroup.org/unix/online.html .
- .PP
- Any typographical or formatting errors that appear
- in this page are most likely
- to have been introduced during the conversion of the source files to
- man page format. To report such errors, see
- https://www.kernel.org/doc/man-pages/reporting_bugs.html .